The present invention relates to a vehicular headlamp having a discharge bulb as its light source.
There has been a recent trend in vehicular headlamps toward adopting discharge bulbs that can emit light of high intensity as the light source bulb.
A vehicular headlamp equipped with a discharge bulb of this type requires a lighting circuit unit to ignite the discharge bulb. Referring to FIG. 6, a lighting circuit unit 102 is in many cases mounted on an outer surface of a bottom wall 104a of a lamp body 104.
Because of a relatively heavy weight associated with the lighting circuit unit 102, deflection deformation tends to occur in the bottom wall 104a of the lamp body 104 when the lighting circuit unit 102 is mounted on the outer surface of the bottom wall 104a. Moreover, a cord insertion opening 104b, used for passing a power feeding cord 108 connecting the lighting circuit unit 102 to a discharge bulb 106, is formed in the bottom wall 104a. A bulb replacement opening 104d for allowing replacement of the discharge bulb 106 is formed in a rear wall 104c of the lamp body 104. These arrangements result in insufficient rigidity in the rear end portion of the bottom wall 104a. This may also result in deflection deformation of the bottom wall 104a due to the weight of the lighting circuit unit 102.
Deflection deformation in the bottom wall 104a can also eventually result in deformation in a front end opening 104e of the lamp body 104, thus leading to failure in the seal between the lamp body 104 and a front lens 110.
In view of the foregoing situation, it is an object of the present invention to provide a vehicular headlamp in which a lighting circuit unit is mounted on the outer surface of a bottom wall of a lamp body and yet which does not induce failure in the seal between the lamp body and front lens.
The present invention achieves the above object by forming a bottom wall extension portion in a bottom wall of a lamp body.
More specifically, a vehicular headlamp of the present invention includes a reflector supporting a discharge bulb housed in a lamp chamber defined by a lamp body, a front lens fitted in an opening at a front end of the lamp body, and a lighting circuit unit for igniting the discharge bulb installed on an outer surface of a bottom wall of the lamp body, and in which a bulb replacement opening for replacing the discharge bulb is formed in a rear wall of the lamp body, and a cord insertion opening, through which a power feeding cord connecting the lighting circuit unit to the discharge bulb passes, is formed in the bottom wall of the lamp body. The vehicular headlamp of the invention is characterized in that a bottom wall extension portion extending rearward beyond the bulb replacement opening is formed at a rear end portion of the bottom wall of the lamp body.
The lighting circuit unit may be constructed so as to be mounted directly, or indirectly via a bracket, unit cover, or other means, on the outer surface of the bottom wall.
The shape of the bottom wall extension portion is not limited so long as it extends rearward beyond the bulb replacement opening.
As described above, the vehicular headlamp according to the present invention has, at the rear end portion of the bottom wall thereof, a bottom wall extension portion which extends rearward beyond the bulb replacement opening, even though the bulb replacement opening is formed in the rear wall of the lamp body and the lighting circuit unit is mounted on the outer surface of the bottom wall of the lamp body, thus providing operational effects as discussed in detail below.
Namely, sufficient rigidity cannot be obtained from the rear end portion of the bottom wall of the lamp body alone since it is adjacent to the bulb replacement opening formed in the rear wall of the lamp body. By providing the bottom wall extension portion according to the present invention it becomes possible to obtain sufficient rigidity for the rear end portion of the bottom wall. This prevents the bottom wall from developing deflection deformation due to the weight of the lighting circuit unit, which in turn prevents deformation of the front end opening in the lamp body. Accordingly, failure of the seal between the lamp body and the front lens is prevented.
Forming the bottom wall extension portion on the bottom wall of the lamp body results in an area of the outer surface of the bottom wall extending rearward. This allows the lighting circuit unit to be mounted at a position further rearward on the outer surface of the bottom wall than would otherwise be possible. This arrangement of the lighting circuit unit permits the mounting of the lighting circuit unit on the bottom wall so that it crosses the rear wall, which prevents deflection deformation in the bottom wall due to the weight of the lighting circuit unit. Should some deflection deformation occur, the front end opening is not influenced by such deformation, thus suppressing failure in the seal between the lamp body and the front lens.
In the vehicular headlamp of the invention equipped with a lighting circuit unit mounted on the outer surface of the bottom wall of the lamp body, failure of the seal between the lamp body and the front lens is effectively prevented.
The aforedescribed structure can further be provided with a plurality of reinforcement ribs extending rearward from the rear wall of the lamp body and which are formed on a top surface of the bottom wall extension portion. With the reinforcement ribs the rigidity of the lamp body is enhanced in the area extending from the rear wall to the bottom wall extension portion. This structure is effective to suppress deflection deformation in the bottom wall due to the weight of the lighting circuit unit. Should any deflection deformation nevertheless occur, the front end opening is not subjected to such deformation, thus preventing failure of the seal between the lamp body and the front lens further effectively.
If the bottom wall extension portion in the aforementioned structure is formed as a folded-back portion having substantially a U-shape in cross section, the rigidity of the bottom wall extension portion is enhanced. This structure is effective in reducing deflection deformation in the bottom wall due to the weight of the lighting circuit unit. Should some deflection deformation nevertheless occur, the front end opening is not subjected to such deformation, thus preventing failure of the seal between the lamp body and the front lens more effectively.
Assuming that a unit cover for covering the lighting circuit unit is mounted on the outer surface of the bottom wall of the lamp body in the aforementioned structure, and the part of the unit cover mounting sealing portion on the bottom wall, which is located rearward of the lighting circuit unit, is formed on the bottom surface of a bottom wall extension portion, which extends rearward from the rear end portion of the bottom wall. As a result, the unit cover mounting sealing portion is protected from deformation, which in turn contributes to obtaining and maintaining a good seal between the unit cover and lamp body.
In this case, the unit cover may be installed separately from the lighting circuit unit mounted on the outer surface of the bottom wall. It may be installed together with the lighting circuit unit on the outer surface of the bottom wall. It may also be assembled with the lighting circuit unit preliminarily so as to be mounted on the outer surface of the bottom wall.